System for displaying required navigation performance on a horizontal situation indicator

ABSTRACT

A display system is provided that renders a horizontal situation indicator that includes required navigation performance (RNP) and estimated position uncertainty (EPU) values rendered non-numerically and in a fairly intuitive manner. A processor receives at least data representative of a desired course of the aircraft, data representative of the RNP for the aircraft, and data representative of the EPU for the aircraft. The processor renders, on a display device, a horizontal situation indicator that includes an aircraft symbol representative of a top-down view of the aircraft, an RNP boundary graphic representative of at least one RNP boundary for the aircraft, and an EPU graphic representative of the EPU for the aircraft. The aircraft symbol is rendered at a position that is representative of actual aircraft position relative to the desired course, and the RNP boundary graphic is rendered at a position relative to the rendered aircraft symbol and comprises a shaded region that shades a portion of the display device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.12/142,531, filed Jun. 19, 2008.

TECHNICAL FIELD

The present invention generally relates to avionic displays and, moreparticularly, to a system for displaying required navigation performanceand estimated position uncertainty on, for example, a horizontalsituation indicator.

BACKGROUND

Commercial aviation regulatory agencies have developed requirednavigation performance (RNP) protocols to facilitate the management ofair traffic. Required navigation performance equipped aircraft cansafely operate along various routes with less separation than previouslyneeded. This can be significant because less separation means that thenumber of aircraft that can safely use a particular airspace mayincrease, and therefore accommodate the increasing demand for airtraffic capacity. Under these protocols, RNP values may be assigned tovarious segments, or legs, of an aircraft's flight plan. For example,during approach an aircraft is typically assigned an RNP value of 0.3nautical miles (nm). Moreover, for enroute portions of a flight aircraftare typically assigned an RNP value of 2.0 nm, for terminal portions theassigned RNP value is typically 1.0 nm, and when flying over the oceanthe RNP value is typically 4.0 or 10.0 nm.

The RNP value defines an airspace within which the aircraft shouldremain for a predetermined percentage (e.g., 95 percent) of the totalflying time. This airspace may be referred to as the RNP ObstacleEvaluation Area or, more simply, the RNP corridor. If the aircraft isRNP capable and if the pilot is appropriately certified, the pilot mayattempt to travel the assigned landing leg while remaining within theRNP corridor. If, during the landing attempt, the aircraft breaches anRNP boundary and the leaves the corridor, a warning indicator (e.g., ahazard light) is presented to the flight crew and the landing may beaborted and attempted again at a later time.

Closely related to RNP, is what is known as the estimated positionuncertainty (EPU). The EPU is basically the value of the total error ofthe aircraft navigation system. It may thus be appreciated that as longas the EPU is less than the current RNP value for the present airspace,then the aircraft can continue operating in the assigned RNP corridor.

Many conventional aircraft display systems include various means fordisplaying current RNP and EPU values to a flight crew. These displaysystems include implementations for displaying the current RNP and EPUvalues both numerically and non-numerically. For example, many displays,such as the horizontal situation indicator (HSI), display the RNP andEPU values numerically, and some attitude display indicators (ADI)display the RNP and EPU values graphically. In both instances, the RNPand EPU values may not be displayed to the flight crew in a highlyintuitive manner.

Hence, it would be desirable to provide a horizontal situation indicatorthat displays RNP and EPU values non-numerically and in a fairlyintuitive manner. The present invention addresses at least this need.

BRIEF SUMMARY

In one embodiment, and by way of example only, an aircraft displaysystem includes a display device and a processor. The processor is inoperable communication with the display device and is adapted to receiveat least data representative of a desired course of the aircraft, datarepresentative of required navigation performance (RNP) for theaircraft, and data representative of estimated position uncertainty(EPU) for the aircraft. The processor is configured, in response to atleast these data, to render a horizontal situation indicator on thedisplay device that includes an aircraft symbol representative of atop-down view of the aircraft, an EPU graphic representative of the EPUfor the aircraft, and an RNP boundary graphic representative of at leastone RNP boundary for the aircraft. The aircraft symbol is rendered at aposition that is representative of actual aircraft position relative tothe desired course, and the RNP boundary graphic is rendered at aposition relative to the rendered aircraft symbol and comprises a shadedregion that shades a portion of the display device.

Furthermore, other desirable features and characteristics of the presentinvention will become apparent from the subsequent detailed descriptionand the appended claims, taken in conjunction with the accompanyingdrawings and the preceding background.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a block diagram of an exemplary embodiment of an avionicsdisplay system;

FIGS. 2-9 depict various configurations of a horizontal situationindicator that may be rendered on a display device of the display systemof FIG. 1.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding background or the following detaileddescription.

A functional block diagram of an exemplary avionics display system 100is depicted in FIG. 1, and includes a processor 102, a plurality of datasources 104, and a display device 106. The processor 102 is in operablecommunication with the data sources 104 and the display device 106. Theprocessor 102 is coupled to receive various types of aircraft data fromthe data sources 104. It will be appreciated that the aircraft data mayvary, but in the depicted embodiment the data includes at least variousaircraft navigation data, data representative of required navigationperformance (RNP) for the aircraft, and data representative of estimatedposition uncertainty (EPU) for the aircraft. The processor 102 isconfigured, in response to at least these data, to render a horizontalsituation indicator on the display device 106.

The processor 102 may be any one (or a plurality) of numerous knowngeneral-purpose microprocessors or application specific processor(s)that operates in response to program instructions. In the depictedembodiment, the processor 102 includes on-board RAM (random accessmemory) 103, and on-board ROM (read only memory) 105. The programinstructions that control the processor 104 may be stored in either orboth the RAM 103 and the ROM 105. For example, the operating systemsoftware may be stored in the ROM 105, whereas various operating modesoftware routines and various operational parameters may be stored inthe RAM 103. It will be appreciated that this is merely exemplary of onescheme for storing operating system software and software routines, andthat various other storage schemes may be implemented. It will also beappreciated that the processor 102 may be implemented using variousother circuits, not just a programmable processor. For example, digitallogic circuits and analog signal processing circuits could also be used.In this respect, the processor 102 may include or cooperate with anynumber of software programs (e.g., avionics display programs) orinstructions designed to carry out various methods, process tasks,calculations, and control/display functions described below.

The data sources 104 supply the above-mentioned aircraft data to theprocessor 102. The data sources 104 may include a wide variety ofinformational systems, which may reside onboard the aircraft or at aremote location. By way of example, the data sources 104 may include oneor more of a runaway awareness and advisory system, an instrumentlanding system, a flight director system, a weather data system, aterrain avoidance and warning system, a traffic and collision avoidancesystem, a terrain database, an initial reference system, a navigationaldatabase, and a flight management system. The data sources 104 may alsoinclude mode, position, and/or detection elements (e.g., gyroscopes,global positioning systems, inertial reference systems, etc.) capable ofdetermining the mode and/or position of the aircraft relative to one ormore reference locations, points, planes, or navigation aids.

As FIG. 1 additionally depicts, the system 100 may also include a userinterface 108. The user interface 108, if included, is in operablecommunication with the processor 102 and is configured to receive inputfrom a user 109 (e.g., a pilot) and, in response to the user input,supply command signals to the processor 102. The user interface 108 maybe any one, or combination, of various known user interface devicesincluding, but not limited to, a cursor control device (CCD) 107, suchas a mouse, a trackball, or joystick, and/or a keyboard, one or morebuttons, switches, or knobs. In the depicted embodiment, the userinterface 102 includes a CCD 107 and a keyboard 111. The user 109 usesthe CCD 107 to, among other things, move a cursor symbol on the displaydevice, and may use the keyboard 111 to, among other things, inputtextual data.

The display device 106 is used to display various images and data, in agraphic, iconic, and a textual format, and to supply visual feedback tothe user 109. It will be appreciated that the display device 106 may beimplemented using any one of numerous known displays suitable forrendering graphic, iconic, and/or text data in a format viewable by theuser 109. Non-limiting examples of such displays include various cathoderay tube (CRT) displays, and various flat panel displays, such asvarious types of LCD (liquid crystal display) and TFT (thin filmtransistor) displays. The display may additionally be based on a panelmounted display, a HUD projection, or any known technology. In anexemplary embodiment, display device 106 includes a panel display. It isfurther noted that the system 100 could be implemented with more thanone display device 106. For example, the system 100 could be implementedwith two or more display devices 106.

No matter the number or particular type of display that is used toimplement the display device 106, it was noted above that the processor102 is responsive to the various data it receives to render a horizontalsituation indicator on the display device 106. A portion of an exemplaryhorizontal situation indicator that may be rendered on the displaydevice 106 is depicted is FIG. 2 and will now be described. Before doingso, it is noted that the depicted horizontal situation indicator 200 ismerely exemplary of one embodiment, and that it could be variouslyimplemented. It is additionally noted that not all of the renderedimages that are depicted in FIG. 2 will be described, and that variousother images that are not depicted in FIG. 2 (or further described)could be rendered on the horizontal situation indicator 200, if neededor desired.

With reference now to FIG. 2, the horizontal situation indicator 200includes, among other images, a compass 202, a course pointer 204, anaircraft symbol 206, a lateral deviation indicator 208, an RNP boundarygraphic 212, and an EPU graphic 214. As is generally known, the compass202 displays the aircraft's magnetic heading, the course pointer 204displays the desired/preset course of the aircraft for the currentsegment of the flight plan, and the aircraft symbol 206, which isrepresentative of a top-down view of the aircraft, displays the actualheading of the aircraft relative to the desired course. The lateraldeviation indicator 208, as is also generally known, is representativeof the lateral deviation of the aircraft from the desired course. InFIG. 2, the aircraft symbol 206 and lateral deviation indicator 208 areboth aligned with the course pointer 204, which indicates that theaircraft is not deviating (or not significantly deviating) from thedesired course.

The depicted RNP boundary graphic 212 and the depicted EPU graphic 214are not rendered on presently known horizontal situation indicators. TheRNP boundary graphic 212 is representative of at least one RNP boundaryfor the aircraft, and the EPU graphic is representative of the EPU forthe aircraft. In FIG. 2, both RNP boundaries 213-1, 213-2 associatedwith the current RNP are rendered on the display. However, as will bedescribed in more detail further below, in some instances only one ofthe RNP boundaries may be rendered. Whether one or both RNP boundariesare rendered, it is noted that the RNP boundary graphic 212 is renderedat a position relative to the rendered aircraft symbol 206. As notedabove, the aircraft symbol 206 is rendered relative to the desiredcourse for the current segment of the aircraft flight plan. Hence, theRNP boundary graphic 212 represents the RNP value assigned to thecurrent segment of the aircraft flight plan. As FIG. 2 depicts, when theaircraft is not deviating from the desired course, the rendered RNPboundary graphic 212 includes both RNP boundaries 213-1, 213-2, whichare rendered symmetrically on both sides of the aircraft symbol 206.

The RNP boundary graphic 212 may be rendered using numerous and variedgraphics. For example, the RNP boundary graphic 212 may be rendered as aseries of separated geometric figures, or as dotted lines, just to namea few. In the depicted embodiment, however, the RNP boundary graphic212, at least when both RNP boundaries 213 are rendered, comprises apair of line segments. One of the line segments 213-1 is rendered to theright of the aircraft symbol 206 and the other line segment 213-2 isrendered to the left of the aircraft symbol 206. In addition to the linesegments, it is seen that outwardly pointing arrowheads may be includedon the ends of the rendered line segments 213.

The EPU graphic 214, like the RNP boundary graphic 212, may be renderedusing numerous and varied graphics. However, also like the RNP boundarygraphic 212, the depicted EPU graphic 214 comprises a pair of linesegments 215-1, 215-2, with one line segment 215-1 rendered to the leftof the aircraft symbol 206 and the other line segment 215-2 rendered tothe right of the aircraft symbol 206. Moreover, in addition to the linesegments, it is seen that inwardly pointing arrowheads may be includedon the ends of the rendered line segments 215. The line segments 215that comprise the EPU graphic 214 are symmetrically disposed on eitherside of the aircraft symbol 206, and are separated from each other by aseparation distance (d) (see FIG. 3) that is proportional to the EPU forthe aircraft. That is, the greater the separation distance (d), thegreater the uncertainty of the aircraft's position. It may thus beappreciated that the horizontal situation indicator 200 that is depictedin FIG. 2 is displayed an aircraft with a relatively strong EPU.Conversely, if the horizontal situation indicator 200 is displayed in anaircraft with a relatively weak EPU, then the EPU graphic 214 will berendered with a greater separation distance, such as the EPU graphic 214that is depicted in FIG. 3.

It was noted above that the RNP boundary graphic 212 is rendered at aposition relative to the aircraft symbol 206. It was additionally notedthat in some instances only one of the RNP boundaries 213 may berendered. Illustrative examples of these features are depicted in FIGS.4-7. Referring first to FIG. 4, the rendered horizontal situationindicator 200 is for a situation in which the aircraft is experiencing aright lateral deviation. In particular, the aircraft is deviating to theright of the desired course in the current flight plan, and isapproaching the right RNP boundary 213-1. As such, the course pointer204 is pointing to the left of the aircraft symbol 206, and the coursedeviation indicator 208 is disposed to the left of the aircraft symbol206 and the course pointer 204. Moreover, the RNP boundary graphic 212comprises only the right RNP boundary 213-1, which is rendered closer tothe aircraft symbol 206 than it was in FIGS. 2 and 3.

If the aircraft were to continue on its course and further increase theright lateral deviation, when a first predetermined lateral deviationdistance is reached, as determined by the processor 102, the renderedhorizontal situation indicator 200 changes. In particular, as FIG. 5depicts not only is the right RNP boundary 213-1 rendered even closer tothe aircraft symbol 206, it is preferably rendered in a different colorthan it was in FIGS. 2-4. It will be appreciated that the color in whichthe RNP boundary graphic 212 is displayed may vary discretely orcontinuously with the lateral deviation of the aircraft. Moreover, it isseen that the processor 102, at least in the depicted embodiment, alsorenders additional graphics on the display device 106. One graphic,which is referred to herein as a corrective graphic 502, includes agraphic representative of a corrective direction 504 and a graphicindicating the lateral deviation distance 506. In the example depictedin FIG. 5 the aircraft is deviating to the right, about 0.8 nauticalmiles (NM) from the desired course, and is very near the right RNPboundary 213-1. As a result, the corrective graphic 502 includes anarrow 504 pointing to the left and a number (e.g., 0.8) 506 indicatingthe lateral deviation distance. The other graphic, which is referred toherein as an RNP annunciator graphic 508, is preferably renderedsimultaneously with the corrective graphic 502.

Turning now to FIGS. 6 and 7, the situation is illustrated for the casein the right lateral deviation is increased even further, so that theaircraft travels completely outside of the RNP corridor. When thisoccurs, as determined by the processor 102, the lateral deviationindicator 206 is rendered at a predetermined position, while the rightRNP boundary 213-1 continues to be rendered in the same color as it wasin FIG. 5, and while the corrective graphic 502 continues to berendered. The position at which the lateral deviation indicator 206 isrendered when the aircraft leaves the RNP corridor may vary. However, inthe depicted embodiment the lateral deviation indicator 206 is renderedat an extreme left-most position within the circumference of therendered compass 202. It will be appreciated, of course, that if theaircraft were to travel outside of the RNP corridor to the left, thatthe lateral deviation indicator 206 would be rendered at an extremeright-most position within the circumference of the rendered compass202.

As FIG. 7 depicts, if the right lateral deviation is increased stillfurther, at some other predetermined distance the right RNP boundary213-1 will be rendered, in the same color as it was in FIGS. 5 and 6, atthe same position as the lateral deviation indicator 208. The right RNPboundary 213-1 will, however, overlap the lateral deviation indicator208 and, at least in the depicted embodiment, obscures the lateraldeviation indicator 208. As with the situations illustrated in FIGS. 5and 6, the corrective graphic 502 continues to be rendered as well. Itis noted that the display system is preferably configured such that anymovement of the movement of the lateral deviation indicator 208, the RNPboundary graphic 212, and/or the EPU boundary graphic 214 is conductedin a smooth manner, and any repositioning of the rendered graphics issmoothly driven to the new location. Thus, there are preferably noabrupt jumps in the positions of the rendered graphics.

The inventive concepts described above not only provide a fairlyintuitive graphic representation of RNP boundaries and the aircraft EPUon the horizontal situation indicator, these concepts may also indicatepositional ambiguity to an aircraft flight crew. For example, if thecurrent EPU for the aircraft is relatively weak, and the aircraft isapproaching one of the RNP boundaries, the horizontal situationindicator 200 rendered on the display device 106 by the processor 102may resemble FIG. 8. The depicted horizontal situation indicator 200shows the aircraft approaching the right RNP boundary 213-1. Moreover,because the EPU is relatively weak, the separation distance (d) betweenthe lines segments 215 of the EPU graphic 214 is relatively large, andthe right line segment 215-1 is rendered to the right of the right RNPboundary 213-1. This clearly represents an ambiguity in the location ofthe aircraft, in that the aircraft could actually be outside of the RNPcorridor.

In another exemplary embodiment, which is depicted in FIG. 9, the RNPboundary graphic 212, at least when both RNP boundaries 213 arerendered, comprises shaded regions that shade portions of the horizontalsituation indicator 200. In this embodiment, one of the regions 213-1 isrendered to the right of the aircraft symbol 206 and the other region213-2 is rendered to the left of the aircraft symbol 206. It will beappreciated that in some embodiments, only a single region 213 may berendered. It will additionally be appreciated that the region (orregions) 213 may be variously shaded. For example, in some embodiments,the region (or regions) 213 may be rendered in various colors or with aplurality of lines (e.g., various hatching or crosshatching patterns) orother geometric symbols. For each instance, the color or patterns arepreferably rendered with suitable transparency to allow that portion ofthe horizontal situation indicator 200 that is being shaded to remainvisible.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims.

What is claimed is:
 1. An aircraft display system, comprising: a displaydevice; and a processor in operable communication with the displaydevice and adapted to receive at least data representative of a desiredcourse of the aircraft, data representative of required navigationperformance (RNP) for the aircraft, and data representative of estimatedposition uncertainty (EPU) for the aircraft, the processor configured,in response to at least these data, to render a horizontal situationindicator on the display device that includes: (i) an aircraft symbolrepresentative of a top-down view of the aircraft, the aircraft symbolrendered at a position that is representative of actual aircraftposition relative to the desired course, (ii) an EPU graphicrepresentative of the EPU for the aircraft, the EPU graphic comprising apair of line segments symmetrically disposed on either side of renderedaircraft symbol and separated from each other by a separation distancethat is proportional to the EPU for the aircraft, one line segmentalways rendered left of the rendered aircraft symbol, and another linesegment always rendered right of the rendered aircraft symbol, and (iii)an RNP boundary graphic representative of at least one RNP boundary forthe aircraft, the RNP boundary graphic rendered at a position relativeto the rendered aircraft symbol and comprising a shaded region thatshades a portion of the display device outside the at least one RNPboundary.
 2. The system of claim 1, wherein the RNP boundary graphic isat least selectively representative of each RNP boundary for theaircraft.
 3. The system of claim 2, wherein the RNP boundary graphic atleast selectively comprises a pair of shaded regions.
 4. The system ofclaim 1, wherein the processor renders the shaded region in a color. 5.The system of claim 4, wherein the color that the processor renders theshaded region is representative of actual aircraft position relative tothe at least one RNP boundary.
 6. The system of claim 1, wherein theprocessor renders the shaded region as a plurality of lines.
 7. Thesystem of claim 1, wherein the processor renders the shaded region as aplurality of geometric symbols.
 8. The system of claim 1, wherein theprocessor is further configured to: determine a lateral deviationdistance of the aircraft from the desired course; and render acorrective graphic if the lateral deviation distance is greater than afirst predetermined lateral deviation distance.
 9. The system of claim8, wherein the processor is further configured to: render the RNPboundary graphic in a first color when the lateral deviation distance isnot greater than the first predetermined lateral deviation distance; andrender at least a portion of the RNP boundary graphic is a second colorwhen the lateral deviation distance is greater than the firstpredetermined lateral deviation distance.
 10. The system of claim 8,wherein the corrective graphic comprises: a graphic representative of acorrective direction; and a graphic indicating the lateral deviationdistance.
 11. The system of claim 8, wherein the processor furtherconfigured to render a lateral deviation indicator on the displaydevice.
 12. The system of claim 11, wherein the processor is furtherconfigured to render the lateral deviation indicator at a predeterminedposition on the display device if the lateral deviation distance isgreater than a second predetermined lateral deviation distance.
 13. Thesystem of claim 12, wherein the processor is further configured torender at least a portion of the RNP boundary graphic at thepredetermined position if the lateral deviation distance is greater thana third predetermined lateral deviation distance.